This is the 8164th most frequent Japanese word.
届か
"届か" is the stem form of "届く," meaning "to reach" or "to arrive."
届かない here expresses an inability for the voice to reach a targeted destination due to distance.
声が遠すぎて届かない。
My voice is too distant and cannot reach.
届く symbolizes the achievement or realization of dreams, metaphorically reaching a desired destination.
夢が届く日を信じています。
I believe in the day my dreams will come true.
届かない indicates that the letter has not successfully reached the recipient, showing an ongoing status of not arriving.